This application claims priority on Japanese Patent Application No. 11-233232 filed on Aug. 19, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a structure of electrical terminals provided in a rechargeable battery pack and an electrical device, such as an electric power tool or a battery charger, for establishing electrical contact therebetween when the pack is attached to the device.
2. Description of the Related Art
Various structures for establishing electrical contact between a rechargeable battery pack and electrical devices, such as electric power tools and battery chargers, are well known in the art. In one such attachment structure for establishing electrical contact, male terminals are mounted on the battery pack, whereas female terminals to be coupled with the male terminals are mounted on the electrical device. Tile contact pressure between the mating terminals of a battery pack and an electrical device need be selected in accordance with the device""s specific operating conditions so as to prevent, for example, heat buildup and/or chattering at the mating terminals due to high voltage, large currents. and/or vibration caused by the operation of such electrical devices. Therefore, different female terminals with different contact pressures have been mounted on different types of electrical devices to obtain a suitable level or degree of contact pressure for each application.
While such a structure of electrical terminals is generally acceptable, it is not free from certain drawbacks, thus leaving room for improvement. One drawback is the increased manufacturing cost and extra time and labor required for manufacturing and mounting different types of female terminals on different devices/apparatuses (to provide different degrees of contact pressure or different contact pressure levels). Moreover, there is a possibility of short circuits occurring between the exposed male terminals provided on the battery pack according to the foregoing structure. In order to prevent short circuits, it would be preferable for the battery pack to be provided with female terminals. If this is the case, however, the battery pack terminals will have one fixed contact pressure level, such that providing male terminals with different thicknesses for electric devices having different operating conditions will be the only means of realizing a range of contact pressure. However, the range of contact pressure afforded by this means is generally limited and thus short of a required level. Alternatively, it is possible to employ male/female terminal combinations having high contact pressure for all terminal connections in order to cover a range of applications that require different levels of contact pressure. In this case, however, the connection between all mating terminals may become exceedingly firm even for the type of applications that do not require very firm terminal connection. An added problem with this solution is that the high contact pressure often results in shortened service life of the terminals.
In view of the above-identified problems, an important object of the present invention is to provide a simple, reliable structure of electrical terminals that offers several levels of contact pressure.
Another object of the present invention is to provide a simple, reliable structure of electrical terminals that effectively prevents short circuits between terminals and cuts manufacturing costs.
The above objects and other related objects are realized by the invention, which provides a structure of electrical terminals for establishing electrical contact between a battery pack and an electrical device by attachment of the battery pack to the electrical device. The structure comprises a plurality of female terminals provided in the battery pack, and a plurality of male terminals provided in the electrical device and adapted to be coupled to the female terminals. In this structure, each of the female terminals includes at least two pairs of elastic plates, each pair of elastic plates being capable of holding one of the male terminals therebetween when the battery pack is attached to the electrical device. Further, the elastic plate pairs of each female terminal are disposed along the path of movement of the male terminal when the battery pack is attached to the electrical device such that the number of elastic plate pairs of each female terminal that hold each male terminal therebetween is determined by the length of the male terminal along the aforementioned path of movement.
This structure of electrical terminals according to the present invention permits the male terminals to be held between a selected number of elastic plate pairs and also permits selection of any appropriate level of contact pressure at the terminals from a plurality of levels, in accordance with the voltage, current, and/or the vibration level in a specific application. This effectively prevents heat buildup and chattering at the terminals. In addition, as the contact pressure on the terminals can be adjusted simply by changing the length of the male terminals without changing the dimensions and/or the shape of the female terminals, a significant cost reduction can be afforded. Moreover, as the female terminals are not exposed to the outside of the battery pack, short circuits can be effectively prevented.
A typical battery pack reaches the end of its service life sooner than the electrical device (e.g., the charger or the tool) with which the pack is used, and needs to be replaced as the cells in the pack deteriorate after a certain number of cycles of charge and discharge. It follows, therefore, that male terminals, which generally have longer life than female terminals, should be employed on the main device to which the pack is attached, with female terminals mounted on battery pack. Unlike conventional structures, the foregoing structure of the invention advantageously employs this logical arrangement of mounting male terminals on the main device and female terminals on the battery pack.
According to one aspect of the present invention, the structure includes two female terminals and two male terminals, each of which male terminals is adapted to be electrically connected to one of the two female terminals. The two female terminals are disposed in parallel to one another and are spaced apart by a first selected distance, and the two male terminals are disposed generally in parallel to one another and are spaced apart by the selected first distance.
According to another aspect of the present invention, each elastic plate includes a parallel portion which extends parallel to the aforementioned path of movement and a contact pressure portion which is bent at an angle to the parallel portion from one end of the parallel portion so as to extend into contact with the paired elastic plate at a point. Furthermore, each of the male terminals includes a strip having a sufficient length along the aforementioned axis to come into contact with at least one of the elastic plate pairs at the aforementioned point, separate the contact pressure portions, and reach beyond the aforementioned point when the battery pack is attached to the electric device.
According to still another aspect of the present invention, the parallel portions of each elastic plate pair are separated from each other by a selected space sufficient to dispose at least part of the strip of the corresponding male terminal therebetween. In addition, each pair of elastic plates is arranged such that, during attachment of the battery pack to the electric device, the male terminal is first slid relative to the electrical device to enter the aforementioned space between the parallel portions, after which the male terminal separates the contact pressure portions at the aforementioned point.
According to yet another aspect of the present invention, each elastic plate includes at least one slit therein formed in the direction substantially parallel to the aforementioned path of movement of the male terminal so as to divide the contact pressure portion into a plurality of elastic pieces.
According to one feature of the present invention, each contact pressure portion is divided into two elastic pieces with an identical width.
In accordance with another feature of the present invention, each contact pressure portion is divided into two elastic pieces with different widths. The slit in each elastic plate provides different natural vibrations for the divided pieces of the elastic plate so as to reduce chattering due to vibration caused, for example, by the operation of the electric power tool.
According to still another feature of the present invention, the strip of each male terminal is sized and dimensioned so as to separate the two pairs of contact plates of the corresponding female terminal.
According to yet another feature of the present invention, the strip of each male terminal is sized and dimensioned so as to separate only one pair of contact plates of the corresponding female terminal.
In accordance with one practice of the present invention, the strip of each male terminal has a substantially rectangular shape.
In accordance with another practice of the present invention, each pair of contact pressure portions applies a selected level of contact pressure on the male terminal when the battery pack is attached to the electric device.
In one embodiment, the electrical device is selected from a group consisting of electric power tools and battery chargers.
Other general and more specific objects of the invention will in part be obvious and will in part be evident from the accompanying drawings and descriptions which follow.